Ram B1500, B2500, B3500, 1999-2003

Intake Air Temperature Sensor

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Operation



The Intake Air Temperature (IAT) sensor determines the air temperature inside the intake manifold. Resistance changes in response to the ambient air temperature. The sensor resistance decreases as the air temperature increases. This provides a signal to the ECM indicating the temperature of the incoming air charge. This sensor helps the ECM to determine spark timing and air/fuel ratio. The IAT is threaded and screws into the intake manifold.


NOTE
Only Multi-port Fuel Injected (MFI) vehicles are equipped with an IAT sensor.

The Intake Air Temperature (IAT) sensor determines the air temperature inside the intake manifold. Resistance changes in response to the ambient air temperature. The sensor resistance decreases as the air temperature increases. This provides a signal to the ECM indicating the temperature of the incoming air charge. This sensor helps the ECM to determine spark timing and air/fuel ratio. The IAT is threaded and screws into the intake manifold.


NOTE
Only Multi-port Fuel Injected (MFI) vehicles are equipped with an IAT sensor.

The two-wire Intake Manifold Air Temperature (IAT) sensor is installed in the intake manifold with the sensor element extending into the air stream.

  1. This is a Negative Thermal Coefficient (NTC), meaning that as the manifold air temperature increases, the resistance (voltage) in the sensor decreases, and vice-versa.
  2.  
  3. The IAT sensor provides an input voltage to the PCM, indicating the density of the air entering the intake manifold based on intake manifold air temperature. When the ignition is turned ON , a 5-volt power circuit is supplied to the sensor from the PCM. The sensor is grounded at the PCM through a low-noise, sensor-return circuit.
  4.  
  5. The PCM uses this input to determine:

    Injector pulse-width (air: fuel ratio)
     
    Ignition timing (to prevent spark knock)
     

  6.  



Click image to see an enlarged view

Fig. IAT sensor installed in the intake manifold of a 5.2L engine. Others similar

Removal & Installation



  1. Disconnect the negative battery cable.
  2.  
  3. Unplug the electrical connector from the sensor.
  4.  
  5. Unscrew the sensor from the intake manifold.
  6.  

To install:

  1. Install the sensor into the intake manifold and tighten it to 20 ft. lbs. (28 Nm).
  2.  
  3. Plug the connector into the sensor.
  4.  
  5. Connect the negative battery cable.
  6.  



Click image to see an enlarged view

Fig. IAT sensor location-2.5L engine shown

Testing




WARNING
Testing the wiring harness with the ECM still connected can cause serious damage to the processor. ALWAYS disconnect the ECM before testing the wiring harness, unless instructed otherwise.

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the engine cover.
  4.  
  5. Unplug the electrical connector at the sensor.
  6.  
  7. Using an ohmmeter, measure the resistance across the two terminals of the sensor. The sensor resistance should be less than 1340 ohms with the engine at normal operating temperature. Replace the sensor if not within specifications.
  8.  
  9. To test the wiring harness, unplug the ECM; test the harness between the proper ECM connector terminal and the sensor connector. Also check the harness between the proper ECM connector terminal and the sensor connector. If resistance is more than 1 ohm, repair the wiring harness.
  10.  
  11. Install the engine cover.
  12.  
  13. Connect the negative battery cable.

    Click image to see an enlarged view

    Fig.



    Click image to see an enlarged view

    Fig.

  14.  


WARNING
Testing the wiring harness with the ECM still connected can cause serious damage to the processor. ALWAYS disconnect the ECM before testing the wiring harness, unless instructed otherwise.

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the engine cover.
  4.  
  5. Unplug the electrical connector at the sensor.
  6.  
  7. Using an ohmmeter, measure the resistance across the two terminals of the sensor. The sensor resistance should be less than 1340 ohms with the engine at normal operating temperature. Replace the sensor if not within specifications.
  8.  
  9. To test the wiring harness, unplug the ECM; test the harness between the proper ECM connector terminal and the sensor connector. Also check the harness between the proper ECM connector terminal and the sensor connector. If resistance is more than 1 ohm, repair the wiring harness.
  10.  
  11. Install the engine cover.
  12.  
  13. Connect the negative battery cable.

    Click image to see an enlarged view

    Fig.



    Click image to see an enlarged view

    Fig.

  14.  

  1. Be sure the ignition is OFF .
  2.  
  3. Disconnect the connector at the IAT sensor.
  4.  
  5. Check resistance across the sensor terminals. Using an input impedance (digital) VOM is recommended.
  6.  
  7. Resistance will vary with temperature, but should be about 18 kilo-ohms at 50ºF (10ºC), decreasing rapidly as temperature increases to about 1kilo-ohms at 176ºF (80ºC) which is near engine operating temperature. If the measured resistance is at or near zero (shorted) or at or near infinity (open), replace the sensor.
  8.  
  9. To test the harness, proceed as follows:
    1. Shut the ignition OFF and disconnect the battery negative cable.
    2.  
    3. Unplug the PCM, test the harness between the proper PCM connector terminal and the sensor connector. Also check the harness between the proper PCM connector terminal and the sensor connector. If resistance is more than 1 ohm, repair the wiring harness.
    4.  

  10.  


WARNING
Testing the wiring harness with the PCM still connected can cause serious damage to the processor. ALWAYS disconnect the PCM before testing the wiring harness, unless instructed otherwise.

  1. Connect the negative battery cable.
  2.  



Click image to see an enlarged view

Fig. Testing the IAT sensor with an ohmmeter connected across the two sensor terminals



Click image to see an enlarged view

Fig. IAT sensor circuit



Click image to see an enlarged view

Fig. IAT sensor's electrical connector terminal identification: (1) BK/LB; (2) BK/RD

 
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